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1. General Principles & Basic Science MCQs

Practice Set 33 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 641

Topic: 1. General Principles & Basic Science

The recommended interval for changing wound vacuum assisted closure (VAC ) dressings is:

. Twice daily
. Daily
. Every 2 days
. Weekly
. Monthly

Correct Answer & Explanation

. Every 2 days

Explanation

The preferred interval for changing VAC dressings is every 2 days. Patients may have significant discomfort with initial dressing changes; however, the pain usually diminishes rapidly.

Question 642

Topic: 1. General Principles & Basic Science

What is the histological difference between avascular necrosis of the femoral head in children versus adults:

. C hildren have less creeping substitution than adults.
. C hildren do not demonstrate osseous collapse.
. Large areas of fibrovascular tissue do not form in children.
. There is no osteoclastic resorption in children.
. C hildren do not have any residual changes after 2 years.

Correct Answer & Explanation

. Large areas of fibrovascular tissue do not form in children.

Explanation

Avascular necrosis models of the femoral head in immature animals show more osteoclastic resorption, fibroblastic response, and little creeping substitution when compared to models of mature animals. Osseous collapse is common, and there are often longterm residual changes in the shape of the femoral head.

Question 643

Topic: 1. General Principles & Basic Science

Which of the following pulse sequences is best for showing anatomy on magnetic resonance imaging (MRI):

. T1-weighted images
. T2-weighted images
. Proton density images
. Fat-suppressed T2-weighted images
. Gradient echo sequence

Correct Answer & Explanation

. T1-weighted images

Explanation

T1-weighted images generally display the best anatomical detail. Fat is bright, and muscle is dark, giving excellent contrast. Cortical bone, tendons, and ligaments are low signal.

Question 644

Topic: 1. General Principles & Basic Science

According to National Institutes of Health (NIH) criteria, what is the minimum number of 15-mm cafa-au-lait macules required as a diagnostic criterion for neurofibromatosis in postpubertal patients:

. One
. Two
. Three
. Four
. Six

Correct Answer & Explanation

. Six

Explanation

The NIH criteria require at least six 15-mm cafa-au-lait macules in postpubertal patients. Cafa-au-lait macules must be larger than 5 mm in prepubertal patients.

Question 645

Topic: Infection, Pharmacology & VTE

A 45-year-old farmer sustains an open tibia fracture with gross soil and manure contamination. Which of the following antibiotic regimens is most appropriate for initial management in the emergency department?

. Cefazolin alone
. Cefazolin and an aminoglycoside
. Cefazolin, an aminoglycoside, and high-dose penicillin
. Vancomycin alone
. Ciprofloxacin alone

Correct Answer & Explanation

. Cefazolin, an aminoglycoside, and high-dose penicillin

Explanation

Farm injuries with gross soil or manure contamination are at high risk for clostridial infection. The addition of high-dose penicillin to a first-generation cephalosporin and an aminoglycoside provides the necessary anaerobic coverage.

Question 646

Topic: Biology, Genetics & Bone Healing

During anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, incorporation of the bony ends into the tunnels occurs primarily via which of the following processes?

. Enchondral ossification
. Creeping substitution
. Fibrocartilage transition
. Intramembranous ossification
. Direct primary bone healing

Correct Answer & Explanation

. Creeping substitution

Explanation

Bone-to-bone healing in tunnels (such as with a BTB graft) occurs via creeping substitution, where osteoclasts resorb the grafted bone and osteoblasts lay down new bone. Conversely, soft tissue grafts heal via a fibrovascular interface.

Question 647

Topic: Biology, Genetics & Bone Healing

Which of the following molecules binds directly to RANK on the surface of osteoclast precursors to stimulate their differentiation into mature osteoclasts?

. Osteoprotegerin (OPG)
. RANKL
. Macrophage colony-stimulating factor (M-CSF)
. Calcitonin
. Parathyroid hormone (PTH)

Correct Answer & Explanation

. RANKL

Explanation

Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), produced by osteoblasts, binds directly to RANK on osteoclast precursors to induce differentiation. Osteoprotegerin (OPG) is a decoy receptor that binds RANKL, inhibiting this process.

Question 648

Topic: 1. General Principles & Basic Science

Which of the following annular pulleys are most biomechanically critical to prevent bowstringing of the flexor tendons in the finger?

. A1 and A3
. A2 and A4
. A3 and A5
. A1 and A5
. A2 and A3

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the most robust and biomechanically critical for preventing bowstringing of the flexor tendons. They are located over the proximal and middle phalanges, respectively.

Question 649

Topic: Biomechanics & Biomaterials

The phenomenon whereby a ligament or tendon demonstrates increasing length over time under a constant applied load is known as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic behavior

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material over time when subjected to a constant load. Stress relaxation is the decrease in stress over time when the material is held at a constant length.

Question 650

Topic: Infection, Pharmacology & VTE
Which of the following best describes the mechanism of action of rivaroxaban, an oral anticoagulant commonly used for venous thromboembolism prophylaxis after total joint arthroplasty?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Indirect Factor Xa inhibitor via antithrombin III
. Platelet ADP receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor, while low-molecular-weight heparins act indirectly via antithrombin III.

Question 651

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a destructive, eccentrically located lytic lesion extending into the epiphysis of the distal femur. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered for downstaging prior to surgery, which of the following agents is most appropriate?

. Imatinib
. Denosumab
. Methotrexate
. Doxorubicin
. Rituximab

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab, a monoclonal antibody against RANKL, is highly effective in treating Giant Cell Tumor of bone by inhibiting the RANKL-mediated osteoclast-like giant cells. It is frequently used to downstage large tumors or treat unresectable disease.

Question 652

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly used in the management of unresectable Giant Cell Tumor of bone. What is its exact mechanism of action?

. Inhibition of matrix metalloproteinases
. Direct cytotoxicity to the neoplastic mononuclear cells
. Binding to the RANK receptor on osteoclasts
. Binding to the RANK ligand (RANKL)
. Inhibition of vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Binding to the RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors. This inhibits the maturation and function of the osteoclast-like giant cells, thereby reducing osteolysis.

Question 653

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what level of tissue strain is required to allow for primary bone healing (direct Haversian remodeling) without callus formation?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Greater than 30%
. Strain level does not affect primary bone healing

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing with callus formation.

Question 654

Topic: 1. General Principles & Basic Science

In flexor tendon anatomy, Camper's chiasm refers to which of the following structures?

. The bifurcation of the FDP tendon
. The bifurcation of the FDS tendon allowing the FDP to pass
. The confluence of the annular pulleys
. The insertion of the lumbrical muscles
. The vincula brevia of the flexor tendons

Correct Answer & Explanation

. The bifurcation of the FDS tendon allowing the FDP to pass

Explanation

Camper's chiasm is the anatomical point in Zone II where the Flexor Digitorum Superficialis (FDS) tendon splits into two slips. This bifurcation allows the Flexor Digitorum Profundus (FDP) tendon to pass through and become superficial.

Question 655

Topic: Infection, Pharmacology & VTE

In the pathophysiology of chronic osteomyelitis, what is the term used to describe the segment of necrotic bone that has become separated from the surrounding viable bone?

. Involucrum
. Cloaca
. Sequestrum
. Brodie's abscess
. Physeal scar

Correct Answer & Explanation

. Sequestrum

Explanation

A sequestrum is a piece of dead, devascularized bone that separates from normal bone in chronic osteomyelitis. The involucrum is the new bone formation that surrounds the sequestrum.

Question 656

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a recurrent giant cell tumor of the distal radius. She is treated with denosumab. What is the specific cellular mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of neoplastic mononuclear cells
. Inhibition of RANKL, preventing osteoclast formation and function
. Stimulation of osteoblast-mediated bone formation
. Cross-linking of DNA leading to cell cycle arrest

Correct Answer & Explanation

. Inhibition of RANKL, preventing osteoclast formation and function

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to RANK on osteoclast precursors. This inhibits osteoclast-mediated bone resorption, which is heavily upregulated by the neoplastic stromal cells in giant cell tumors.

Question 657

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans and vertically aligned type II collagen fibers?

. Superficial zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans. It has collagen fibers aligned perpendicular to the joint surface to resist high compressive loads.

Question 658

Topic: 1. General Principles & Basic Science

During the incorporation of a cortical bone allograft, the process of creeping substitution occurs. Which of the following accurately describes this mechanism?

. Simultaneous bone resorption and formation by cutting cones
. Formation of bone directly on the allograft surface without prior resorption
. Rapid revascularization through pre-existing Haversian canals within 3 days
. Osteoinduction via BMP release from the allograft
. Replacement of graft with fibrous tissue prior to ossification

Correct Answer & Explanation

. Simultaneous bone resorption and formation by cutting cones

Explanation

Creeping substitution in cortical bone involves osteoclastic resorption followed closely by osteoblastic bone formation via cutting cones. It is a significantly slower process compared to cancellous bone incorporation.

Question 659

Topic: 1. General Principles & Basic Science

Following a complete peripheral nerve transection, what is the earliest histologic change seen in the denervated skeletal muscle?

. Type I fiber hypertrophy
. Atrophy of Type II fibers initially, followed by Type I
. Uniform atrophy of both Type I and Type II fibers
. Target cell formation due to central myofibril loss
. Fatty infiltration and fibrosis

Correct Answer & Explanation

. Target cell formation due to central myofibril loss

Explanation

The earliest histologic sign of denervation is the formation of target cells, which exhibit a central loss of myofibrils and oxidative enzymes. This precedes the eventual grouped atrophy seen in chronic denervation.

Question 660

Topic: 1. General Principles & Basic Science
During the remodeling phase of medial collateral ligament (MCL) healing, which biochemical transition is most prominent?
. Replacement of Type I collagen with Type III collagen
. Replacement of Type III collagen with Type I collagen
. Decreased collagen cross-linking
. Increased synthesis of glycosaminoglycans
. Conversion of elastic fibers to collagen

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

During the remodeling phase of ligament healing, the initial, weaker Type III collagen produced during the proliferative phase is gradually replaced by stronger, more highly cross-linked Type I collagen.

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